Diffuse bright field illumination system for a barcode reader

ABSTRACT

One aspect of the present disclosure is related to a barcode reader that includes a bright field illumination system, a dark field illumination system, and an additional illumination system that is better able to illuminate an area of the reader&#39;s field of view between the far zone (where bright field illumination is optimal) and the close zone (where dark field illumination is optimal). In this “center zone,” the dark field illumination may not be bright enough and the bright field illumination may not be diffuse enough for reading a barcode.

TECHNICAL FIELD

The present disclosure relates generally to barcode readers. Morespecifically, the present disclosure relates to a barcode reader thatincludes multiple illumination systems, including a diffuse bright fieldillumination system.

BACKGROUND

A barcode is an optical machine-readable representation of information.Devices for identifying or extracting information from barcodes aregenerally referred to as barcode readers (or barcode scanners). Animage-based barcode reader includes a camera for capturing an image of abarcode to be read. The camera includes a focusing lens that focuseslight reflected from a target area onto a photo sensor array. Once animage of a barcode has been captured by the camera, a decoder processesthe image and extracts the information contained in the barcode.

A barcode reader may include both a bright field illumination system anda dark field illumination system for illuminating a target area. Abright field illumination system typically includes multipleillumination elements (e.g., light-emitting diodes (LEDs)) withrefracting and/or diffusing optics designed to direct illuminationtowards the target area essentially parallel to the optical axis (i.e.,a line originating from the center of the focusing lens and extendingoutward into the center of the camera's field of view). A bright fieldillumination system may provide optimal illumination for a “far zone” ofthe camera's field of view, i.e., an area that is located relatively faraway from the reader.

A dark field illumination system typically includes multiple LEDs withoptics that project illumination from the sides of the reader towardsthe optical axis at an angle no more than 45 degrees from the plane thatis perpendicular to the optical axis. A dark field illumination systemmay provide optimal illumination for a “close zone” of the field ofview, i.e., an area that is nearly in contact with the reader.

SUMMARY

The present invention provides a barcode reader including anillumination system that illuminates the barcode using light that exitsan optical substrate after traveling between a front major surface and aback major surface of the optical substrate in a direction transverse toan optical axis of a camera.

One aspect of the present disclosure is related to a barcode reader thatincludes a bright field illumination system, a dark field illuminationsystem, and an additional illumination system that is better able toilluminate an area of the reader's field of view between the far zone(where bright field illumination is optimal) and the close zone (wheredark field illumination is optimal). In this “center zone,” the darkfield illumination may not be bright enough and the bright fieldillumination may not be diffuse enough for reading a barcode.

A diffuse bright field illumination system in accordance with thepresent disclosure may include an optic comprising light-diffusingcharacteristics and a plurality of illumination elements located onedges of the optic. The plurality of illumination elements may directillumination into the optic. The light-diffusing characteristics of theoptic may diffuse the illumination, and a majority of the diffusedillumination may exit a front major surface of the optic.

According to one aspect of the invention, there is provided a barcodereader, comprising a bright field illumination system, a diffuse brightfield illumination system, and a dark field illumination system. Thebright field illumination system directs bright field illumination intoa field of view of the barcode reader substantially parallel to anoptical axis of the barcode reader. The bright field illumination isoptimal for barcode reading within a far zone of the field of view. Thediffuse bright field illumination system directs diffuse bright fieldillumination into the field of view substantially parallel to theoptical axis. The diffuse bright field illumination is more diffuse thanthe bright field illumination. The diffuse bright field illumination isoptimal for barcode reading within a center zone of the field of view.The dark field illumination system directs dark field illumination intothe field of view at an angle no more than 45 degrees relative to aplane that is perpendicular to the optical axis. The dark fieldillumination is optimal for barcode reading within a close zone of thefield of view.

Alternatively or additionally, the bright field illumination is notsufficiently diffuse and the dark field illumination is not sufficientlybright to provide optimal illumination for barcode reading within atleast part of the center zone.

Alternatively or additionally, the center zone overlaps with the farzone and also with the close zone.

Alternatively or additionally, the diffuse bright field illuminationsystem includes an optic comprising light-diffusing characteristics anda plurality of illumination elements located on corner edges of theoptic. A front major surface and a back major surface of the optic arelocated in a plane that is substantially perpendicular to the opticalaxis. The back major surface and other edge surfaces of the optic arecoated with an opaque reflective coating or covered with a reflectivematerial. The back major surface may contain features that uniformlyredirect the light coming from the edge to exit from the front majorsurface in directions substantially parallel to the optical axis.

Alternatively or additionally, the optic comprises a non-uniform indexof refraction.

Alternatively or additionally, the bright field illumination systemincludes a first plurality of illumination elements positioned behind orbefore first optics. The diffuse bright field illumination systemincludes a second plurality of illumination elements and a second opticpositioned between the second plurality of illumination elements. Thedark field illumination system includes a third plurality ofillumination elements positioned behind or before second optics.

Alternatively or additionally, the barcode reader includes a unitaryoptical component. The bright field illumination system includes a firstplurality of illumination elements positioned behind curved regions ofthe unitary optical component. The diffuse bright field illuminationsystem includes a second plurality of illumination elements and a secondoptic positioned between the second plurality of illumination elements.The dark field illumination system includes a third plurality ofillumination elements positioned behind diffusion regions of the unitaryoptical component.

According to another aspect of the invention, a diffuse bright fieldillumination system for a barcode reader, includes an optic comprisinglight-diffusing characteristics and a plurality of illumination elementslocated on edges of the optic. The plurality of illumination elementsdirect illumination into the optic, the light-diffusing characteristicsof the optic diffuse the illumination, and a majority of the diffusedillumination exits a front major surface of the optic.

Alternatively or additionally, a back major surface and other externaledge surfaces of the optic are coated with an opaque reflective coating.

Alternatively or additionally, the optic comprises a non-uniform indexof refraction.

Alternatively or additionally, the optic includes a substrate having afirst index of refraction and particles embedded within the substrate.The particles have a second index of refraction that is different thanthe first index of refraction.

Alternatively or additionally, the front major surface and a back majorsurface of the optic are smooth and planar.

Alternatively or additionally, the front major surface of the optic issmooth and planar and a back major surface of the optic is non-planar.

Alternatively or additionally, the optic includes a first materialhaving a first index of refraction, the optic includes a second materialhaving a second index of refraction that is different than the firstindex of refraction, and the first material is in contact with thesecond material along a non-planar surface.

Alternatively or additionally, the front major surface and a back majorsurface of the optic are non-planar.

Alternatively or additionally, the optic further comprises an aperturethrough which a field of view is visible to a camera of the barcodereader.

Alternatively or additionally, the optic further comprises a pluralityof apertures that permit illumination from another illumination systemwithin the barcode reader to be directed into a field of view withoutbeing affected by the optic.

Alternatively or additionally, the optic further includes a plurality ofapertures that permit targeting illumination to be projected into afield of view without being affected by the optic.

Alternatively or additionally, aperture surfaces within the optic arecoated with an opaque reflective coating.

According to a further aspect of the invention, there is provided abarcode reader, including a dark field illumination system and a diffusebright field illumination system. The dark field illumination systemincluding a first plurality of illumination elements and a plurality ofprism optics. Each illumination element within the first plurality ofillumination elements directs first illumination substantially parallelto an optical axis of the barcode reader toward a distinct one of theplurality of prism optics, which redirects the first illumination towardthe field of view at a desired angle. The diffuse bright fieldillumination system including a second plurality of illuminationelements and an optic including light-diffusing characteristicspositioned between the second plurality of illumination elements. Thesecond plurality of illumination elements direct second illuminationinto the optic. The light-diffusing characteristics of the optic diffusethe second illumination.

Alternatively or additionally, the plurality of prism optics includechamfered ends of a plurality of light pipes.

Alternatively or additionally, a front major surface and a back majorsurface of the optic are located in a plane that is substantiallyperpendicular to the optical axis and the second plurality ofillumination elements are located on edges of the optic.

According to another aspect of the invention, there is provided abarcode reader, including a housing, a camera, and an illuminationsystem. The camera is located within the housing and is configured tocapture an image of a barcode within a field of view of the camera. Thefield of view is directed along an optical axis. The illumination systemis configured to illuminate the barcode while the camera captures theimage of the barcode. The illumination system includes at least onelight source and an optical substrate. The optical substrate has frontand back major surfaces arranged generally perpendicular to the opticalaxis, and between which light introduced from the at least one lightsource is transferred by total internal reflection primarily in adirection transverse to the optical axis. The optical substrate includesone or more extraction features configured to extract light from theoptical substrate and into the field of view.

Alternatively or additionally, the at least one light source introduceslight into an edge of the optical substrate between the front and backmajor surfaces.

Alternatively or additionally, the at least one light source introduceslight into the optical substrate through the back major surface.

Alternatively or additionally, the optical substrate includes at leastone aperture associated with at least one of the camera, the at leastone light source, and at least one targeting light source.

Alternatively or additionally, the optical substrate includes areflective backing adjacent the back major surface.

Alternatively or additionally, the reflective backing is attached to theback major surface.

Alternatively or additionally, the one or more extraction featuresintroduce a variation in an index of refraction.

Alternatively or additionally, the variation in the index of refractionincludes at least one of one or more particles, a planar surface withinthe optical substrate, a variation in the surface topography of the backmajor surface, and a variation in the surface topography of the frontmajor surface.

Alternatively or additionally, the one or more extraction features aredistributed non-uniformly throughout the optical substrate.

Alternatively or additionally, the one or more extraction features aredistributed throughout the optical substrate such that light isuniformly emitted from the front major surface of the optical substrate.

Alternatively or additionally, the one or more extraction features aredistributed throughout the optical substrate such that light isnon-uniformly emitted from the front major surface of the opticalsubstrate in a desired intensity pattern.

Alternatively or additionally, the illumination system additionallyincludes at least one secondary light source. The light from the atleast one secondary light source emitted by the illumination systemconverges at a point along the optical axis different from the pointalong the optical axis that light emitted by the illumination systemfrom the at least one light source converges.

Alternatively or additionally, the illumination system additionallyincludes at least one secondary light source. The light from the atleast one secondary light source is emitted by the illumination systemat an angle closer to parallel to the optical axis than the light fromthe at least one light source emitted by the illumination system.

Alternatively or additionally, the illumination system additionallyincludes at least one tertiary light source. The light from the at leastone tertiary light source is emitted by the illumination system at anangle closer to perpendicular to the optical axis than the light fromeither the at least one light source or the at least one secondary lightsource that is emitted by the illumination system.

Alternatively or additionally, the light from the at least one tertiarylight source is emitted by the illumination system at an angle no morethan 45° from a plane perpendicular to the optical axis.

Alternatively or additionally, a shape of at least one of the frontmajor surface and the back major surface is at least one of concave,convex, and parabolic.

Alternatively or additionally, the shape of at least one of the frontmajor surface and the back major surface is not symmetrical about aplane perpendicular to the optical axis.

Alternatively or additionally, the optical substrate has an annularshape.

Alternatively or additionally, the camera is located near a center ofthe optical substrate.

Alternatively or additionally, the optical substrate includes an outeredge and an inner edge and the at least one light source introduceslight into the outer edge of the optical substrate.

Alternatively or additionally, the optical substrate comprises an outeredge comprising a chamfered surface configured to reflect light onto apath relatively perpendicular to the optical axis.

Alternatively or additionally, the optical substrates further includesan inner edge including a surface relatively parallel to the opticalaxis such that a portion of the light exits the optical substratesthrough the inner edge at an angle no more than 45° from a planeperpendicular to the optical axis.

Alternatively or additionally, the at least one light source comprises alight emitting diode (LED).

Alternatively or additionally, the camera further comprises a lenslocated along the optical axis.

A number of features are described herein with respect to embodiments ofthe invention; it will be appreciated that features described withrespect to a given embodiment also may be employed in connection withother embodiments.

The invention includes the features described herein, including thedescription, the annexed drawings, and, if appended, the claims, whichset forth in detail certain illustrative embodiments. These embodimentsare indicative, however, of but a few of the various ways in which theprinciples of the invention may be employed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top-down view of a barcode reader in accordance with thepresent disclosure.

FIGS. 2A-2E are front views of different embodiments of an opticalsubstrate within the barcode reader shown in FIG. 1.

FIGS. 3A-3F illustrates cross-sectional views of different embodimentsof the optic, taken along line A-A in FIGS. 2A-2C.

FIGS. 4A-4C are cross-sectional views of alternative embodiments of theoptical substrate.

FIG. 5 is a top-down view of another embodiment of a barcode reader inaccordance with the present disclosure.

FIG. 6 is a top-down view of another embodiment of a barcode reader inaccordance with the present disclosure.

FIG. 7 is a top-down view of an additional embodiment of a barcodereader in accordance with the present disclosure.

FIGS. 8A-8B are cross-sectional views of tertiary light sourcesilluminating the optical substrate in two embodiments of the barcodereader.

FIG. 9 illustrates one configuration of a barcode reader in accordancewith the present disclosure.

FIG. 10 illustrates an example of a method that may be performed by theillumination selection circuitry of the barcode reader in accordancewith the present disclosure.

FIG. 10A illustrates an example showing the relative size of a testimage compared with a subsequent image.

FIG. 11 illustrates another example of a method that may be performed bythe illumination selection circuitry in accordance with the presentdisclosure.

FIG. 12 illustrates one example of a single test image comprising aplurality of window images.

FIG. 12A illustrates another example of a single test image comprising aplurality of window images.

FIG. 13 illustrates another example of a method that may be performed bythe illumination selection circuitry in accordance with the presentdisclosure.

FIGS. 14A and 14B illustrate a plurality of test images comprising aplurality of window images.

FIG. 15 illustrates another example of a method that may be performed bythe illumination selection circuitry in accordance with the presentdisclosure.

FIG. 16 illustrates another example of a method that may be performed bythe illumination selection circuitry in accordance with the presentdisclosure.

FIG. 17 illustrates another example of a method that may be performed bythe illumination selection circuitry in accordance with the presentdisclosure.

FIG. 18 illustrates various components that may be utilized in a barcodereader.

DETAILED DESCRIPTION

The present invention provides a barcode reader for imaging a barcodeusing diffuse light. The barcode reader illuminates a barcode using anillumination system including an optical substrate. Light introducedinto the optical substrate by at least one light source propagatesbetween a front major surface and a back major surface in a directiontransverse to an optical axis of a camera. Light is mixed by totalinternal reflection as its travels within the optical substrate and oneor more extraction features included in the optical substrate allowlight to be removed from the optical substrate in a directed intensitypattern. By allowing the light to mix as it propagates within theoptical substrates, the propagating light loses any structure impartedonto it by the one or more light sources. By illuminating the barcodewith unstructured light, it is possible to more accurately and quicklyread the information contained in the imaged barcode.

FIG. 1 is a top-down view of a barcode reader 100 in accordance with thepresent disclosure. The barcode reader 100 includes a housing 101, acamera 103, and an illumination system 105. The barcode reader 100illuminates a barcode with the illumination system 105 and captures animage of the barcode using the camera 103.

The camera 103 is located within the housing 101 and is configured tocapture an image of a barcode within a field of view 106 of the camera103. The field of view 106 of the camera 103 is directed along anoptical axis 114 of the camera 103. The camera may include a photosensor array 102 and a lens 104 that focuses illumination reflected fromobjects (e.g., a barcode) within the field of view 106 onto the photosensor array 102. The optical axis of the camera 103 may be the opticalaxis of the lens 104. The camera 103 may be located near a center of theoptical substrate 122 in one or more of the vertical dimension and thehorizontal dimension.

As will be understood by one of ordinary skill in the art, the camera103 may comprise any device capable of capturing an image of a field ofview. For example, the photo sensor array 102 may comprise any detectorcapable of measuring or quantifying light incident on the pixel array ofthe detector. The detector may comprise, for example, an image sensor,CCD sensor, CMOS sensor, or any device capable of measuring orquantifying light incident on the pixel array of the detector.Similarly, the lens may comprise a single lens or series of lensescapable of focusing light onto the photo sensor array 102. Furtherdetails regarding specific embodiments of the camera 103 are discussedbelow.

The illumination system 105 is configured to illuminate the barcodewhile the camera 103 captures an image of the barcode. The illuminationsystem 105 includes at least one light source 120 and an opticalsubstrate 122 including one or more extraction features. The opticalsubstrate 122 has a front major surface 140 and a back major surface 138arranged generally perpendicular to the optical axis 114. Light isintroduced from the at least one light source 120 between the frontmajor surface 140 and the back major surface 138 (FIGS. 3A-3F and4A-4C). The introduced light is transferred by total internal reflectionthrough the optical substrate 122 between the front major surface 140and back major surface 138 in a direction transverse to the optical axis114. For example, in FIG. 1, light propagates through the opticalsubstrate 122 in a directional generally perpendicular to the opticalaxis 114. In an alternative embodiment depicted in the cross sectionalviews of the optical substrate 122 of FIGS. 3B and 3C, the at least onelight source 120 introduces light into the optical substrate 122 throughthe back major surface 138. In this example, the optical substrate 122has a chamfered surface 125 that reflects light 191 through totalinternal reflection towards the optical axis 114.

As shown in FIG. 1, the front view of the optical substrate 122 shown inFIG. 2A, and the cross sectional views of the optical substrate 122shown in 3A, and 3D to 3H the at least one light source 120 may bepositioned adjacent an edge 186 of the optical substrate 122. In thisconfiguration, as shown in FIG. 2A, light may exit the at least onelight source 120 through a single light emitting surface (light leavingthe light emitting surface is represented by arrows 190 a-d).

Alternatively, as shown in FIG. 2B the front view of the opticalsubstrate 122 shown in FIG. 2B, and the cross sectional views of theoptical substrate 122 shown in FIGS. 3B and 3C, the at least one lightsource 120 may be positioned on the back major surface 138 at locations121 a-d. In this configuration light may exit the at least one lightsource 120 through a single light emitting surface (light leaving thelight emitting surface) and be reflected from the chamfered edge 125 anddirected towards the optical axis in direction 191.

Alternatively, as shown in FIG. 2C, the at least one light source 120may be positioned within a recess 121 in the optical substrate 122. Inthis example, the at least one light source 120 may emit light frommultiple light emitting surfaces and the light from all of the lightemitting surfaces may enter the optical substrate 122.

Referring briefly to FIG. 2D, the at least one light source 120 may bereduced to four (4) light sources, each of which is arranged on oneexterior edge of the substrate 122 at a location that is not centered onthe edge. For example, light source 120 a may be on a side edge lowerthan center while light source 120 c may be on the opposing side higherthan center. Light source 120 d may be on the top edge to the right ofcenter which light source 120 b may be on the bottom edge to the left ofcenter.

Referring to FIGS. 1 and 2A, the one or more light sources 120 maycomprise multiple LEDs 120 a-d. As will be understood by one of ordinaryskill in the art, the one or more light sources 120 may comprise anysuitable light emitting device. Further, the multiple light sources 120may emit illumination with different characteristics. For example, aportion of the light sources 120 may be white LEDs while another portionmay be red LEDs, or LEDs of another color.

As shown in FIG. 1, the optical substrate 122 may comprise asubstantially flat plate. For example, the optical substrate 122 maycomprise a clear and colorless acrylic substrate which may be made fromany other material suitable for transferring light by total internalreflection. The optical substrate 122 may be positioned within thereader 100 so that a front major surface 140 and a back major surface138 of the optical substrate 122 are located in a plane that issubstantially perpendicular to the optical axis 114. In one embodiment,“substantially perpendicular” means within five degrees of perpendicularwhile in an alternative embodiment substantially perpendicular meanswithin 15 or 20 degrees of perpendicular.

The light emitted from the optical substrate 122 may have differentcharacteristics depending on the characteristics of the opticalsubstrate 122. For example, the optical substrate 122 may utilizerefraction, diffusion, prismatic effect, and/or total internalreflection to direct more diffuse illumination 124 into the field ofview 106. Depending on the properties of the optical substrate 122 andthe at least one light source 120, the illumination system may bereferred to as a diffuse bright field illumination system. The diffusebright field imaging system may also be called a midfield illuminationsystem or a medium field illumination system.

In one embodiment, the light emitted from the optical substrate 122 maybe emitted substantially parallel to the optical axis 114. For example,light may be emitted within 10 degrees of parallel to the optical axis114. Illumination having a smaller angle spread around the optical axis114 may be referred to herein as diffuse bright field illumination 124.

Alternatively, referring to FIGS. 4A to 4C, the optical substrate 122may be shaped such that the shape of the front major surface 140 and/orthe back major surface 138 is concave, convex, parabolic, or somecombination thereof. For example, as shown in FIG. 4A, the opticalsubstrate 122 has a generally concave shape front major surface 140 anda convex shaped back major surface 138, while in FIG. 4B, the opticalsubstrate 122 has a generally convex shape front major surface 140 and aconcave shaped back major surface 138. The shape of at least one of thefront major surface and the back major surface need not be symmetrical,but may be asymmetrical about a plane perpendicular to the optical axis114. In FIG. 4C, the front major surface 140 may include three generallyplanar sections with the central section being generally perpendicularto the optic axis 114 and two generally planar sections adjacent to, andon opposing sides, of the central section being at an angle relative tothe optic axis. In one embodiment the angle may be no greater than 45degrees. In this embodiment the back major surface 138 may also includecorresponding sections with the central section being generallyperpendicular to the optic axis 114 and two generally planar sectionsadjacent to, and on opposing sides, of the central section being at anangle relative to the optic axis. In one embodiment, the angle of thetwo opposing sides of the back major surface 138 may be the same angleas the two opposing sides of the front major surface 140. In anotherembodiment the angle may be different.

The light emitted by the configurations shown FIGS. 4A 4C may be emittedat different angles relative to the optical axis compared to theillumination system 105 depicted in FIG. 1. the illumination system 105with these configurations is a diffuse bright field illumination systemproviding uniform illumination for barcodes applied to a concave/convexsurface.

In embodiments in which the illumination system 105 emits diffuse light,the illumination may be optimal for reading a barcode that has areflective surface that is located in a near zone 158 and/or a centerzone 126 of the field of view 106. The center zone 126 may begin at acenter zone starting boundary 128 and end at a center zone endingboundary 130. The center zone starting boundary 128 is closer to thereader 100 than a far zone starting boundary 118. For example, thecenter zone starting boundary 128 may be located approximately 25 mmaway from the reader 100. The center zone ending boundary 130 may belocated within the far zone 116. Thus, the center zone 126 and the farzone 116 may overlap.

As discussed, the optical substrate 122 may be positioned between theone or more light sources 120. For example, as shown in FIGS. 1, and 2Athe one or more light sources 120 may be located along an edge 186 ofthe optical substrate 122 that is located between the front majorsurface 140 and the back major surface 138. The one or more lightsources 120 introduce light into the edge 186 of the optical substrate.In FIG. 1, light is introduced from the one or more light sources 120into the optical substrate 122 in a direction generally perpendicular tothe optical axis 114 and generally towards the optical axis 114.

For example, as shown in FIG. 3B the one or more light sources 120 maybe located along an edge of the back major surface 138 of the opticalsubstrate 122 with the chamfered edge 125 reflecting illumination in adirection between the front major surface 140 and the back major surface138 in a direction generally perpendicular to the optical axis 114 andgenerally towards the optical axis 114.

The center of the optical substrate 122 may include an opening 133 or anaperture 132 through which objects (such as a barcode) within the fieldof view 106 may be visible to the lens 104 and the photo sensor array102. As shown in FIGS. 2A, 2B, and 2C, the aperture may be rectangularand of sufficient size such that the optical substrate 122 is not withinthe field of view 106 of the camera 103. As shown in FIG. 2E, theoptical substrate 122 may have an approximately annular shape where thecenter opening 133 of the annular optical substrate 122 is circular andof sufficient size such that the optical substrate 122 is not within thefield of view 106 of the camera 103.

With continued reference to FIG. 2C, the optical substrate 122 may havean annular shape that includes an outer edge 186 and an inner edge 187.In the depicted embodiment multiple light sources 120 a-d are positionedon the back major surface 140 of the optical substrate 122 and inputlight into the optical substrate 122 through the back major surface 140.For example, the light sources 120 a-d may be positioned as shown inFIG. 3B or 3C. In FIGS. 3B and 3C, the light sources 120 a-d input lightthrough the back major surface 140 in a direction approximately parallelto the optical axis 114. After entering the optical substrate 122, thelight is reflected by a chamfered surface 125 of the outer edge 186. Thechamfered surface 125 is configured to reflect light onto a pathrelatively perpendicular to the optical axis 114. In another embodiment(not shown) in which the optical substrate has an annular shape, lightenters the optical substrate 122 through the outside edge 186 in adirection approximately perpendicular to the optical axis 114.

To prevent the optical substrate 122 from functioning simply as a lightpipe or light guide, the optical substrate 122 includes one or moreextraction features 142 configured to extract light from the opticalsubstrate 122 and into the field of view 106. The extraction features142 may introduce a variation in the index of refraction (i.e., alocation of non-uniform index of refraction) of the optical substrate122. Each extraction feature 142 functions to disrupt the total internalreflection of the propagating light that is incident on the extractionfeature.

As described above with respect to FIGS. 2A and 2D, the illumination 190a-d directed into the edge 186 of the optical substrate 122 generallypropagates through the optical substrate 122 due to total internalreflection. Any illumination 190 a-d that is incident on the one or moreextraction features 142 may be diffused with a first portion beingdiffused at an angle such that the illumination continues propagatingwithin the optical substrate 122 (based on total internal reflection)and a second portion may be diffused at an angle (i.e., an escape angle)that overcomes total internal reflection, “escapes” the surface, and isdirected into the field of view 106.

The extraction of illumination through the front major surfaceintroduced by the extraction features 142 may comprise at least one of:i) one or more particles within the substrate 122, ii) a planar surfacewithin the optical substrate 122, iii) a variation in the surfacetopography of the back major surface 138, and iv) a variation in thesurface topography of the front major surface 138. For example, in FIGS.3A and 3B, the optical substrate 122 is embedded with particles 142having an index of refraction greater or less than the optical substrate122. As light travels from the edge 186 of the optical substrate 122through total internal reflection towards a center of the opticalsubstrate 122, the particles 142 disrupt the total internal reflectionof the light, causing a portion of the propagating light to exit throughthe front major surface 140.

The extraction features 142 may be configured to extract light in adefined intensity profile over the front major surface 140, such as auniform intensity profile, and/or a defined light ray angledistribution. In FIG. 3A, the one or more extraction features 142 aredistributed non-uniformly throughout the optical substrate 122. In thisexample, the one or more extraction features 142 are distributedthroughout the optical substrate such that light is uniformly emittedfrom the front major surface 140 of the optical substrate 122. Forexample, the extraction features 142 may be spread throughout theoptical substrate 122 in concentrations that increase with distance fromthe at least one light source 120.

Alternatively, in FIG. 3B, the one or more extraction features 142 maybe distributed uniformly or non-uniformly throughout the opticalsubstrate. In this example, the one or more extraction features aredistributed throughout the optical substrate such that light is notuniformly emitted from the front major surface 140 of the opticalsubstrate 122. Instead the light is emitted from the front major surface140 in a desired intensity pattern. While not shown, the one or moreextraction features 142 may be distributed in alternative patterns thatresult in the light being emitted from the front major surface 140 ofthe optical substrate 122 having a more structured appearance (i.e., anon-uniform intensity pattern).

As shown in FIGS. 3C and 3E, the extraction features 142 may alsocomprise a surface variation in the topography of at least one of thefront major surface 140 and the back major surface 138. In the depictedembodiment of FIG. 3C, the one or more extraction features 142 comprisevariations in the back major surface 138 of the optical substrate 122.In this example, the front major surface 140 of the optical substrate122 is smooth and planar, while the back major surface 138 includes atopography of convex and concave indentations and protrusions. In thedepicted embodiment of FIG. 3E, both the back major surface 138 and thefront major surface 140 include extraction features 142 comprisingconvex and concave indentations and protrusions.

These embodiments are configured to result in a homogenous output oflight from the front major surface 140.

The convex and concave indentations and protrusions may be: i) features142 with specific optical properties, such as micro lenses formed by,for example, molding or laser cutting; or ii) features 142 with nospecific optic properties (i.e. random) such as a roughened surfaceformed by any of a textured tool or sanding of the surface aftermolding. Further, the shape, density, or other optical properties of theextraction features 142 may increases with distance from the lightsource 120 a-d in order to produce uniform illumination from the opticalsubstrate.

Turning to FIGS. 3D and 3F, the one or more extraction features 142comprise a surface within the optical substrate 122. In this embodiment,the optical substrate 122 may be made of two different materials 546,548. These materials 546, 548 may have different indices of refraction,and they may be in contact with one another. In FIG. 3E, the contact isalong a surface forming the one or more extraction features 142. In FIG.3F the contact is along a surface of convex and concave shapes, eitherpatterned or random. Refraction at the one or more extraction features142 directs illumination towards the front major surface 140 of theoptical substrate 122 at an angle where the illumination exits the frontmajor surface 140 towards the field of view 106. As a variation to theseembodiments, the materials 546, 548 may have the same index ofrefraction, but a material with a different index of refraction may besandwiched between the materials 546, 548 at the non-planar contactsurface 550.

As will be understood by one of ordinary skill in the art, the opticalsubstrate 122 and the extraction features 142 are not limited to thesedescribed embodiments. Other embodiments of the optical substrate 122including extraction features 142 are also within the scope of thepresent disclosure.

In all of these embodiments, to further increase the quantity ofillumination exiting through the front major surface 140, a reflectivebacking 144 may be applied to the back major surface 138. The reflectivebacking 144 may be applied uniformly such that it covers the entire backmajor surface 138. The reflective backing 144 reduces the amount oflight that escapes through the back major surface 138 by reflectinglight back inward into the optical substrate 122. In another embodiment,a cladding film (not shown) having an index of refraction less than theindex of refraction of the optical substrate 122 is adjacent the backmajor surface 138. The cladding film reduces the amount of light thatescapes by reflecting light inward through total internal reflection.Similarly, all edges and surfaces of the optical substrate 122 (exceptfor the edges 186 where the one or more light sources 120 a-d projectillumination into the optical substrate 122) may also be coated with areflective backing 144.

Depending on the properties of the illumination system 105, the lightemitted by the illumination system 105 from the one or more lightsources 120 may not be sufficiently bright to provide optimalillumination for reading a barcode that is located farther away from thereader 100 than the center zone ending boundary 130. For this reason, asshown in FIG. 1, the illumination system may comprise at least onesecondary light source 108. The at least one secondary light source 108may be referred to as a direct bright field illumination system or a farfield illumination system. Light from the at least one secondary lightsource 108 that is emitted by the illumination system 105 may convergeat a point on the optical axis 114 that is different from the pointalong the optical axis 114 that light from the at least one light source120 converges. For example, the light may be emitted by the illuminationsystem 105 at an angle closer to parallel to the optical axis 114, forexample at a convergence angle of approximately 70 degrees) than thelight from the at least one light source 120 that is emitted by theillumination system 105.

The at least one secondary light source may comprise one or more LEDs108 a-b, which may be positioned behind refracting and/or diffusingoptics 110 a-b. The one or more secondary light sources 108 a-b maydirect illumination 112 into the field of view 106 substantiallyparallel to the optical axis 114 but with a slight convergence angle.For example, the one or more secondary light sources 108 a-d may directillumination into the field of view 106 at an angle from 0-30 degreesfrom the optical axis 114. This illumination 112 may be referred toherein as direct bright field illumination 112 or far fieldillumination. As indicated above, the optical axis 114 is a lineoriginating from the center of the focusing lens 104 and extendingoutward into the center of the field of view 106.

Light emitted by the illumination system from the at least one secondarylight source may be better suited for reading a barcode with a diffusesurface such as a paper label. Light emitted by the illumination systemfrom the at least one secondary light source may also be optimal forreading a barcode that is located in a far zone 116 of the field of view106, i.e., an area of the field of view 106 that is relatively far awayfrom the reader 100. In other words, light from the at least onesecondary light source may have sufficient intensity to illuminate abarcode that is located within the far zone 116. The far zone 116 maybegin at a far zone starting boundary 118 and end at a far zone endingboundary 119. In one implementation, the far zone starting boundary 118may be located about 75 mm away from the reader 100. The bright fieldillumination 112 may not be sufficiently diffuse to provide optimalillumination for reading a barcode that has a reflective surface. Forlonger range reading, the illumination system may additionally comprisea focus lens associated with the at least one secondary light source inorder to provide illumination for reading a barcode that is locatedfarther away from the reader 100 than the far zone ending boundary 119.

The optical substrate 122 may further include apertures 134 a-b thatpermit the direct bright field illumination 112 (from the at least onesecondary light source 108 a-b) to be directed into the field of view106 without being affected by the optical substrate 122. Further yet,the optical substrate 122 may include apertures 136 a-b that permittargeting illumination from targeting light sources 109 a-b (FIG. 1)mounted behind the optical substrate 122 to be projected into the fieldof view 106 without being affected by the optical substrate 122.

The secondary light source may include secondary light sources 108 a,108 b mounted within the housing 101. Secondary light sources 108 a, 108b are the interior of the housing 101 and may be behind tertiary lightsources 152 a-b (discussed herein) which are behind diffusors 154 a, 154b. The secondary light sources 108 a, 108 b may be in front of thetertiary light sources 152 a, 152 b. As will be discussed with respectto FIG. 6, the secondary light sources may also be positioned in frontof the illumination sources 120 a, 120 b but behind the tertiary lightsources 152 a-b.

The surfaces of the apertures 132, 134 a-b, 136 a-b within the opticalsubstrate 122 may be coated with an opaque reflective material (notshown). This material may cause illumination within the opticalsubstrate 122 that is incident on the surface of a particular apertureto be reflected back into the optical substrate 122 regardless of itsangle of incidence. Reflecting illumination back into the opticalsubstrate 122 prevents illumination from exiting the optical substrate122 through the surface of any aperture at an angle where it wouldilluminate the region behind the optical substrate 122, such as directlyilluminating the lens 104 and degrading the quality of the image of anobject within the field of view 106.

Referring again to FIG. 1, the illumination system 105 may also includeat least one tertiary light source 152. Light from the at least onetertiary light source 152 may be emitted by the illumination system 105at an angle closer to perpendicular to the optical axis 114 than thelight from either of the at least one light source 120 or the at leastone secondary light source 108 that is emitted by the illuminationsystem 105. The at least one tertiary light source 152 may comprisemultiple LEDs 152 a-b. Additional optics 154 a-b may also be associatedwith the at least one tertiary light source 152 to direct illuminationto the field of view 106. The additional optics 154 a-b may utilizerefraction, diffusion, prismatic effect, and/or total internalreflection to direct illumination 156 a-b into the field of view 106.

The at least one tertiary light source 152 may be referred to as a darkfield illumination system or a near field illumination system. Lightemitted by the illumination system from the at least one tertiary lightsource may be referred to herein as dark field illumination 156 a-b.Light from the at least one tertiary light source may be emitted by theillumination system (i.e., the dark field illumination 156 a-b) at anangle no more than 45° from a plane perpendicular to the optical axis114.

The dark field illumination 156 a-b may be optimal for reading a barcodethat is located within a close zone 158 of the field of view 106. Theclose zone 158 may begin at a close zone starting boundary 160 and mayend at a close zone ending boundary 162. The close zone startingboundary 160 may be closer to the reader 100 than the center zonestarting boundary 128. The close zone starting boundary 160 maycorrespond to the face of the reader 100. The close zone ending boundary162 may be within the center zone 126. Thus, the close zone 158 and thecenter zone 126 may overlap. However, the dark field illumination 156a-b may not be sufficiently bright to provide optimal illumination forreading a barcode that is located farther away from the reader 100 thanthe close zone ending boundary 162.

In the embodiment shown in FIG. 1, the at least one tertiary lightsource 152 a-b is mounted on circuit boards at the sides of the readerhousing 101. The optics 154 a-b may comprise lenses, gratings, ordiffusion material that diffuses the illumination 156 a-b from the atleast one tertiary light source 152.

With reference to FIG. 5, an alternative embodiment of the barcodereader 100 is depicted. In this embodiment, the at least one tertiarylight source 152 a-b is mounted on a circuit board 792 that issubstantially perpendicular to the optical axis 114. Illumination 776a-b from the at least one tertiary light sources 152 a-b is directedsubstantially parallel to the optical axis 114 toward prism optics 778a-b. More specifically, the at least one tertiary light source 152 a-bmay project illumination 776 a-b into light pipes 788 a-b, which usetotal internal reflection to propagate the illumination 776 a-b towardthe prism optics 778 a-b. The prism optics 778 a-b are used to re-directthe illumination 776 a-b toward the field of view 106 at the desiredangle.

The light pipes 788 a-b may comprise chamfered ends 778 a-b. Thesechamfered ends 778 a-b may serve as the prism optics 778 a-b thatre-direct the illumination 776 a-b toward the field of view 706. Each ofthe chamfered ends 778 a-b may be angled such that total internalreflection redirects the illumination 776 a-b at a non-zero angle (e.g.,45°) relative to the plane that is perpendicular to the optical axis714. The illumination 776 a-b may exit the light pipes 788 a-b throughthe side facing the optical axis 714. It should be appreciated that thelight pipes 778 a-778 b are shown in cross section and may be on eachside of the camera (all four sides, left, right, top, bottom) or mayeven form an annular ring around the field of view of the camera.

Turning to FIG. 6, another embodiment of the barcode reader 100 isshown. In this embodiment, the optical substrate 880 forms a protectivewindow over optical substrate 122 and replaces the optics 110 a-b, and154 a-b of FIG. 1. In this example, the at least one tertiary lightsource 152 comprise LEDs 152 a-b positioned behind diffusion regions 884a-b of the optical substrate 880. The diffusion regions 884 a-b directdark field illumination 856 a-b from the LEDs 152 a-b into the field ofview 806. The curved regions 882 a-b provide structural support for thediffusion regions 884 a-b as well as focusing the illumination projectedfrom secondary illumination sources 108 a, 108 b—or secondaryillumination sources 115 a, 115 b.

Turning to FIG. 7, another embodiment of the barcode reader 100 isshown. In this embodiment, the optical substrate 881 forms a protectivewindow over optical substrate 122 and replaces the optics 110 a-b ofFIG. 1.

As shown in FIG. 8A, the illuminators 884 may include an opticalsubstrate into which illumination 815 a-b is projected by two side fireilluminators 813 a-b. The illumination 815 a-b is internally reflectedwithin the substrate 811 and extracted as diffuse illumination 156 fromthe optical substrate 811. The optical substrate 811 may have any of thecharacteristics, and extraction features, as the optical substrate 122as described with respect to FIGS. 1, 2A-D, 3A-F, and 4A-C, as well asreflective coatings such that illumination propagates between a frontmajor surface and aback major surface of optic 811 and it extractedthrough the front major surface as illumination 156.

As shown in FIG. 8B, the illuminators 884 may include an opticalsubstrate 821 into which illumination 825 a-b is projected through theback major surface by two illuminators 819 a-b. The illumination 825 a-bis reflected from chamfered surfaces such that it propagates between thefront major surface and the back major surface and is extracted asdiffuse illumination 156 from the optical substrate 821. As with opticalsubstrate 811, the optical substrate 821 may have any of thecharacteristics, and extraction features, as the optical substrate 122as described with respect to FIGS. 1, 2A-D, 3A-F, and 4A-C, as well asreflective coatings such that illumination propagates between a frontmajor surface and aback major surface of optic 811 and it extractedthrough the front major surface as illumination 156.

The diffusion regions 884 a-b direct dark field illumination 856 a-bfrom the LEDs into the field of view 806. The curved regions 882 a-bprovide structural support for and focusing the illumination projectedfrom secondary illumination sources 108 a, 108 b—or secondaryillumination sources 115 a, 115 b. Posts 883 a and 883 b providestructural support for the dark field illumination systems 884 a-b andprevent illumination from entering into the curved regions 882 a-b.

The previous discussion has been directed to a barcode reader thatincludes three different light sources: at least one secondary lightsource (a bright field illumination system—positioned at any of: i)closer to the field of view (i.e. in front of) than the tertiary lightsources, ii) behind the tertiary light sources but in front of thediffuse bright field illumination sources; or iii) behind the diffusebright field illumination sources and optical substrate 122), at leastone light source (a diffuse bright field illumination system), and atleast one tertiary light source (a dark field illumination system).

It should also be appreciated that each of these illumination sourcesmay generate illumination with different characteristics. For example,the diffuse bright field illumination may be white LEDs (illuminationwith intensity across a wide spectrum of wave lengths) while thetertiary light source and the secondary light source may be red LEDs(i.e. intensity at 660 nm).

These three illumination systems can be independently operated such thata barcode can be read with the illumination system that provides thebest illumination for reading the barcode. The discussion that followsincludes some examples of how this may be accomplished. Although some ofthese examples involve only two different illumination systems, thoseexamples may be extended to barcode readers that include three (or more)different illumination systems.

Photo sensor arrays can be operated in two modes: a rolling shutter modeof operation and a global shutter mode of operation. In the globalshutter mode of operation, all photo sensors within the array (i.e., allrows of the array) may be exposed at the same time for the duration ofan exposure period. During the exposure period charge may accumulate oneach photo sensor based on the incident illumination. At the end of theexposure period the charge may be read out row by row.

In the rolling shutter mode of operation, two different signals may beutilized: a reset signal and a read signal. The reset signal may affectall of the photo sensors in a row and may put the photo sensors in astate to convert light intensity into an electrical signal. The readsignal may similarly be applied to all of the photo sensors in a row,and may cause the electrical signals from each photo sensor in the rowto be read electronically.

To capture an image, the reset signal may be applied sequentially toeach row in the photo sensor array, starting at the top of the photosensor array and proceeding row-by-row to the bottom of the photo sensorarray. At some fixed time interval after this reset process has started,the readout process may begin, i.e., the read signal may be appliedsequentially to each row in the photo sensor array. The “exposure” of arow of photo sensors refers to the period of time between the row ofphoto sensors being reset and the row of photo sensors being read.

The exposure time may be expressed as an integer value. The actualexposure time may be the integer value multiplied by the duration oftime required to read out a single row. As such, the size of the rolling“exposure zone” may be the quantity of lines represented by the integervalue. For example, if the exposure value is 10, when exposure of row 1is complete and read out of row 1 starts, row 11 would start exposureand be exposed for the duration of read out of rows 1 to 10.

In both the global shutter mode of operation and the rolling shuttermode of operation, windowing may be utilized. When windowing isutilized, only a portion of the photo sensor array (typically ahorizontal window) is used for exposure and read out. Because only aportion of the photo sensor array is used for exposure, imaging abarcode using windowing is faster than using the entire photo sensorarray. For example, for the global shutter mode a window of 128 rowsbetween rows 128 and 256 may be simultaneously exposed for an exposureduration, and the accumulated charge may be read out row by row. In thisexample, there is no read out of rows below 128 or above 256. In therolling shutter mode, a window of 128 rows between rows 128 and 256 maybe exposed and read out using a rolling exposure zone as discussedabove. Again there would not be any read out of rows below 128 or above256.

As indicated above, the present disclosure relates generally totechniques for selecting the type of illumination that will be mostsuitable for reading a barcode in a particular situation. FIG. 9illustrates one configuration of a barcode reader 902 in accordance withthe present disclosure.

The barcode reader 902 includes a photo sensor array 904. The photosensor array 904 may be capable of operating in accordance with a globalshutter mode of operation and/or a rolling shutter mode of operation, asdiscussed above. The photo sensor array 904 may also be capable ofutilizing windowing, as discussed above.

The barcode reader 902 also includes a plurality of illumination systems906 a-b having different illumination characteristics. Some examples ofdifferent illumination characteristics include the angle of illuminationwith respect to an optical axis, the intensity of illumination, thewavelength of illumination, diffusion characteristics of theillumination, etc.

The plurality of illumination systems 906 may include a bright fieldillumination system 906 a and a dark field illumination system 906 b.The bright field illumination system 906 a may provide illuminationhaving characteristics designed to illuminate a target area that islocated relatively far away from the reader 902. Conversely, the darkfield illumination system 906 b may provide illumination havingcharacteristics designed to illuminate a target area that is locatedrelatively close to the reader 902.

Of course, the number of illumination systems 906 a-b shown in FIG. 9 isfor purposes of example only. In an alternative configuration, a barcodereader may include more than two different illumination systems.Alternatively still, a barcode reader in accordance with the presentdisclosure may include a single illumination system that is configuredto provide illumination having different illumination characteristics(e.g., by changing the intensity, wavelength, angle, and/or diffusioncharacteristics of the illumination).

The barcode reader 902 also includes illumination selection circuitry908. The illumination selection circuitry 908 may be configured toperform operations that are related to selecting the type ofillumination that will be most suitable for reading a barcode in aparticular situation.

FIG. 10 illustrates an example of a method 1000 that may be performed bythe illumination selection circuitry 908 in accordance with the presentdisclosure. The circuitry 908 may be configured to cause the photosensor array 904 to capture 1002 at least one test image. For example,the photo sensor array 904 may capture 1002 a single test image 1210(see, e.g., FIGS. 11 and 12). Alternatively, the photo sensor array 904may capture 1002 a plurality of test images 1210 a-b (see, e.g., FIGS.13, 14A and 14B).

The photo sensor array 904 may utilize windowing when the test image(s)are captured 1002, so that the test image(s) may each be smaller than afull photo sensor array image. As used herein, the term “full photosensor array image” refers to an image that is captured when an entirephoto sensor array 904 is exposed and read out. Thus, a full photosensor array image may include pixels corresponding to all of the photosensors in the photo sensor array 904. In contrast, the test image(s)may each include pixels corresponding to only a subset (i.e., less thanall) of the photo sensors in the photo sensor array 904. Capturing atest image that includes pixels corresponding to only a subset of thephoto sensors in the photo sensor array 904 takes less time thancapturing a full photo sensor array image.

The test image(s) may include at least a portion of a barcode. That is,only a portion of a barcode (i.e., less than an entire barcode) may bevisible in the test image(s). Alternatively, an entire barcode may bevisible in the test image(s).

The test image(s) may include a plurality of window images. As usedherein, the term “window image” refers to an image that is smaller thana full photo sensor array image. In one possible configuration, a singletest image 1210 may be captured, and the single test image 1210 maycomprise a plurality of window images 1212 a-b. (See, e.g., FIG. 12.) Inanother possible configuration, a plurality of test images 1410 a-b maybe captured, and each test image 1410 may comprise a window image 1412.(See, e.g., FIGS. 14A-14B.)

Returning to FIG. 10, the circuitry 908 may be configured to provide1004 illumination for each window image from a distinct configuration ofthe plurality of illumination systems 906 a-b. For example, if thebarcode reader 902 includes a bright field illumination system 906 a anda dark field illumination system 906 b, the test image(s) may include atleast two different window images. The illumination for capturing afirst window image may be provided solely by the bright fieldillumination system 906 a, and the illumination for capturing a secondwindow image may be provided solely by the dark field illuminationsystem 906 b.

Alternatively, multiple illumination systems 906 a-b may be activated atthe same time with various permutations of balanced intensity. Forexample, the illumination for capturing the first window image may beprovided by the bright field illumination system 906 a at 60% power andthe dark field illumination system 906 b at 40% power. The illuminationfor capturing the second window image may be provided by the brightfield illumination system 906 a at 40% power and the dark fieldillumination system 906 b at 60% power.

The circuitry 908 may also be configured to determine 1006 a selectedillumination system configuration. The selected illumination systemconfiguration may be a configuration of the plurality of illuminationsystems 906 a-b that yielded a window image having highest quality amongthe plurality of window images.

Generally speaking, the quality of an image of a barcode may be measuredin terms of the contrast between the light cells and the dark cellswithin the barcode. A barcode image having relatively high contrastbetween dark cells and light cells may be considered to have higherquality than another barcode image having relatively low contrastbetween dark cells and light cells.

The terms “dark cells” and “light cells” are used herein becausebarcodes have traditionally been printed with ink. This gives barcodesthe appearance of having dark cells (the portion that is printed withink) and light cells (the unprinted substrate background, typicallywhite). However, with direct part mark technology, ink is not alwaysused and other techniques (e.g., laser/chemical etching and/or dotpeening) may be used instead. Such techniques may be utilized to createa barcode by causing different portions of a substrate to have differentreflective characteristics. When these different portions of thesubstrate are imaged, the resulting barcode image may have theappearance of including dark cells and light cells. Therefore, as usedherein, the terms “dark cells” and “light cells” should be interpretedas applying to barcodes that are printed with ink as well as barcodesthat are created using other technologies.

The contrast between the dark cells and the light cells in a barcode maybe a function of illumination. Ideally, it is desirable to provideillumination that is consistent across the barcode and of an intensitysuch that the exposure of the image yields both dark cells and lightcells that are within the dynamic range of the photo sensor array 904.This yields better contrast than any of the following: (i) a dimly litbarcode; (ii) a brightly lit barcode wherein the image is washed outbeyond the dynamic range of the photo sensor array 904; (iii) anunevenly lit barcode with bright washed out spots; or (iv) a barcodeilluminated with illumination that is not compatible with thereflectivity characteristic(s) of the cells of the barcode. An exampleof (iv) is that illumination directed from the sides of the field ofview yields a higher contrast image of a barcode formed by etchingtechnology than does illumination parallel to the optical axis.

If the quality of a window image is measured in terms of contrast,determining 1006 the selected illumination system configuration mayinclude determining which window image of the plurality of window imageshas highest contrast between light and dark cells of the barcode, anddetermining which configuration of the plurality of illumination systems906 a-b was activated when the window image having the highest contrastwas captured.

Alternatively, the quality of the window images may be measured in termsof the presence of desired barcode features and/or patterns. A score ormetric may be calculated for each window image. A particular windowimage's score/metric may indicate the number of desired barcode featuresand/or patterns that are detected in the window image. For example, ahigher score/metric may indicate a greater number of desired barcodefeatures and/or patterns (or vice versa). If the quality of the windowimages is measured in this way, then determining 1006 the selectedillumination system configuration may include determining which windowimage of the plurality of window images has the most favorablescore/metric based on features or patterns of the barcode, anddetermining which configuration of the plurality of illumination systems906 a-b was activated when the window image having the most favorablescore/metric was captured.

The circuitry 908 may also be configured to cause the photo sensor array904 to capture 1008 a subsequent image using the selected illuminationsystem configuration. The subsequent image may be captured using aglobal shutter or a rolling shutter mode of operation. As indicatedabove, the test image(s) may include only a portion of a barcode (i.e.,only part of the barcode may be visible within the test image(s)).However, the subsequent image may include an entire barcode (i.e., theentire barcode may be visible within the subsequent image).

The subsequent image may be a full photo sensor array image. That is,the subsequent image may include pixels corresponding to all of thephoto sensors in the photo sensor array 904. Alternatively, thesubsequent image may include pixels corresponding to substantially allof the photo sensors in the photo sensor array 904. In this context, thephrase “substantially all” of the photo sensors in the photo sensorarray 904 may mean at least 95% of the photo sensors in the photo sensorarray 904.

Alternatively still, the size of the subsequent image may be larger thanthe test image(s), but less than a full photo sensor array image. Forexample, referring to FIG. 10A, a test image 1010 may include pixelscorresponding to a first subset 1018 of the photo sensors in the photosensor array 904, and the subsequent image 1016 may include pixelscorresponding to a second subset 1020 of the photo sensors in the photosensor array 904. The second subset 1020 may be larger than the firstsubset 1018. However, the second subset 1020 may not include all of thephoto sensors in the photo sensor array 904.

The size and location of the second subset 1020 may be determined basedon defined rules. For example, the size and location of the secondsubset 1020 may correspond to the size and location of a previously readbarcode. Alternatively, the size and location of the second subset 1020may be determined by estimating the border of the barcode 1022 in thetest image 1010 based on characteristics of the barcode 1022 visible inthe test image 1010, and then setting the size and location of thesecond subset 1020 to include the estimated border.

As another example, if the dark field illumination system 906 b yields ahigher quality window image than the bright field illumination system906 a, then the entire photo sensor array 904 may be utilized to capturethe subsequent image 1016 (because the “up close” barcode 1022 will belarger). Conversely, if the bright field illumination system 906 ayields a higher quality window image than the dark field illuminationsystem 906 b, then a subset 1020 (e.g., a central portion) of the photosensors within the photo sensor array 904 may be utilized to capture thesubsequent image 1016 (because the “far away” barcode 1022 will besmaller).

FIG. 11 illustrates another example of a method 1100 that may beperformed by the illumination selection circuitry 908 in accordance withthe present disclosure. The circuitry 908 may be configured to cause thephoto sensor array 904 to capture 1102 a single test image 1210 (shownin FIG. 12) of at least a portion of a barcode using a rolling shuttermode of operation. Windowing may be utilized, so that the test image1210 may be smaller than a full photo sensor array image.

The circuitry 908 may be configured to cycle through 1104 a plurality ofconfigurations of the plurality of illumination systems 906 a-b whilethe test image 1210 is being captured, so that each illumination systemconfiguration is activated for a distinct time period while the testimage 1210 is being captured and is not otherwise activated while thetest image 1210 is being captured. Consequently, the test image 1210 mayinclude a plurality of window images 1212 a-b. Each window image 1212may correspond to a distinct band (e.g., a horizontal band) within thetest image 1210, and each window image 1212 may correspond to a distinctillumination system configuration.

For example, during exposure of a first section 1214 a of the photosensor array 904, the bright field illumination system 906 a may beactivated, while the dark field illumination system 906 b may bedeactivated. During exposure of a second section 1214 b of the photosensor array 904, the dark field illumination system 906 b may beactivated, while the bright field illumination system 906 a may bedeactivated. (Both the bright field illumination system 906 a and thedark field illumination system 906 b may be activated during exposure ofthe section of the photo sensor array 904 between the first section 1214a and the second section 1214 b, as the transition is made from onesystem to the other.)

In this example, the test image 1210 that is captured includes twodistinct bands. The band corresponding to the first section 1214 a ofthe photo sensor array 904 is captured using illumination solely fromthe bright field illumination system 906 a. Thus, this window image 1212a may indicate the suitability of the bright field illumination system906 a for capturing an image of a barcode. The band corresponding to thesecond section 1214 b of the photo sensor array 904 is captured usingillumination solely from the dark field illumination system 906 b. Thus,this window image 1212 b may indicate the suitability of the dark fieldillumination system 906 b for capturing a barcode.

In the example just described, there is one window image 1212 for eachillumination system 906. However, under some circumstances multiplewindow images may be captured for one or more of the illuminationsystems 906. For example, during exposure of a first section of thephoto sensor array 904, the bright field illumination system 906 a maybe activated, while the dark field illumination system 906 b may bedeactivated. During exposure of a second section of the photo sensorarray 904, the dark field illumination system 906 b may be activated,while the bright field illumination system 906 a may be deactivated.During exposure of a third section of the photo sensor array 904, thebright field illumination system 906 a may be activated at reduced power(e.g., 50%), while the dark field illumination system 906 b may bedeactivated. The test image in this example may include three windowimages corresponding to three distinct bands within the test image. Thefirst window image may indicate the suitability of the bright fieldillumination system 906 a for capturing an image of a barcode. Thesecond window image may indicate the suitability of the dark fieldillumination system 906 b for capturing an image of a barcode. The thirdwindow image may indicate the suitability of the bright fieldillumination system 906 a, operating at reduced power, for capturing animage of a barcode.

Alternatively, both illumination systems 906 a-b may be activated at thesame time with various permutations of balanced intensity. For example,the band corresponding to the first section 1214 a of the photo sensorarray 904 may be captured using illumination from the bright fieldillumination system 906 a powered at 60% and the dark field illuminationsystem 906 b powered at 40%. The band corresponding to the secondsection 1214 b of the photo sensor array 904 may be captured usingillumination from the bright field illumination system 906 a powered at40% and the dark field illumination system 906 b powered at 60%.

In FIG. 12, the width of the test image 1210 and the width of the windowimages 1212 a, 1212 b within the test image 1210 are shown as beingequal to the width of the photo sensor array 904. As shown in FIG. 12A,however, the width of the test image 1210′ and the width of the windowimages 1212 a′, 1212 b′ within the test image 1210′ may alternatively beless than the width of the photo sensor array 904.

Returning to FIG. 11, the circuitry 908 may also be configured todetermine 1106 a selected configuration of the plurality of illuminationsystems 906 a-b. The selected illumination system configuration may bethe configuration of the plurality of illumination systems 906 a-b thatyielded a window image 1212 having highest quality among the pluralityof window images 1212 a-b. The circuitry 908 may also be configured tocause the photo sensor array 904 to capture 1108 a subsequent imageusing the selected illumination system configuration.

FIG. 13 illustrates another example of a method 1300 that may beperformed by the illumination selection circuitry 908 in accordance withthe present disclosure. The circuitry 908 may be configured to cause thephoto sensor array 904 to capture 1302 a plurality of test images 1410a-b (shown in FIGS. 14A-6B) of at least a portion of a barcode. Theplurality of test images 1410 a-b may be captured 1302 using a rollingshutter mode of operation or using a global shutter mode of operation.As shown in FIG. 14A, the plurality of test images 1410 a-b maycorrespond to different sections of the photo sensor array 904. In otherwords, a first section of the photo sensor array 904 may be exposed andread out in order to capture the first test image 1410 a, and a secondsection of the photo sensor array 904 may be exposed and read out inorder to capture the second test image 1410 b. Alternatively, as shownin FIG. 14B, the plurality of test images 1410 a-b may correspond to thesame section of the photo sensor array 904. In other words, the samesection of the photo sensor array 904 may be exposed and read out inorder to capture both test images 1410 a-b.

The circuitry 908 may be configured to cycle through 1304 a plurality ofconfigurations of the plurality of illumination systems 906 a-b whilethe plurality of test images 1410 a-b are being captured, so that eachillumination system configuration is used as the sole source ofillumination for at least one test image 1410. Each test image 1410 maytherefore be considered to be a window image 1412 corresponding to aparticular illumination system configuration. In other words, theplurality of test images 1410 a-b may comprise a plurality of windowimages 1412 a-b. Each window image 1412 may correspond to a differentone of the plurality of test images 1410 a-b. Each window image 1412 mayalso correspond to a different one of the plurality of illuminationsystem configurations.

For example, a first test image 1410 a and a second test image 1410 bmay be captured. The bright field illumination system 906 a may beactivated and the dark field illumination system 906 b may bedeactivated while the first test image 1410 a is being captured.Conversely, the dark field illumination system 906 b may be activatedand the bright field illumination system 906 a may be deactivated whilethe second test image 1410 b is being captured. The first test image1410 a may be considered to be a window image 1412 a corresponding tothe bright field illumination system 906 a. The second test image 1410 bmay be considered to be a window image 1412 b corresponding to the darkfield illumination system 906 b.

Alternatively, the bright field illumination system 906 a may beactivated at 60% power and the dark field illumination system 906 b maybe activated at 40% power while the first test image 1410 a is beingcaptured. The bright field illumination system 906 a may be activated at40% power and the dark field illumination system 906 b may be activatedat 60% power while the second test image 1410 b is being captured.

Returning to FIG. 13, the circuitry 908 may also be configured todetermine 1306 a selected illumination system configuration. Theselected illumination system configuration may be the configuration ofthe plurality of illumination systems 906 a-b that yielded a windowimage 1412 having highest quality among the plurality of window images1412 a-b. The circuitry 908 may also be configured to cause the photosensor array 904 to capture 1308 a subsequent image using the selectedillumination system configuration.

In the examples that are shown in FIGS. 14A and 14B, the width of thetest images 1410 a-b and window images 1412 a-b are equal to the widthof the photo sensor array 904. Alternatively, however, the width of thetest images and window images may be less than the width of the photosensor array 904.

FIG. 15 illustrates another example of a method 1500 that may beperformed by the illumination selection circuitry 908 in accordance withthe present disclosure. The illumination selection circuitry 908 may beconfigured to cause the photo sensor array 904 to capture 1502, usingone or more test images, a plurality of window images of at least aportion of a barcode.

The plurality of window images may include a first window image and asecond window image. The illumination selection circuitry 908 may beconfigured to provide 1504 illumination having a first set ofillumination characteristics for capturing the first window image andillumination having a second set of illumination characteristics(different than the first set of illumination characteristics) forcapturing the second window image. In this context, a “set ofillumination characteristics” may include multiple illuminationcharacteristics, or only a single illumination characteristic. Someexamples of different illumination characteristics were described above.

Different illumination systems 906 a-b may be utilized to provideillumination having different illumination characteristics.Alternatively, a single illumination system 906 may be utilized, but theillumination system may be capable of providing illumination havingdifferent illumination characteristics.

The illumination selection circuitry 908 may also be configured todetermine 1606 a selected set of illumination characteristics. Theselected set of illumination characteristics may be the set ofillumination characteristics that yielded a window image having highestquality among the plurality of window images.

As indicated above, the quality of a window image may be measured interms of image contrast. Therefore, determining 1506 the selected set ofillumination characteristics may include determining which window imageof the plurality of window images has highest contrast between light anddark cells of the barcode, and determining which set of illuminationcharacteristics was utilized when the window image having the highestcontrast was captured.

Alternatively, as indicated above, the quality of a window image may bemeasured in terms of the presence of desired barcode features and/orpatterns. Therefore, determining 1506 the selected set of illuminationcharacteristics may include determining which window image of theplurality of window images has the most favorable score/metric based onfeatures or patterns of the barcode, and determining which set ofillumination characteristics was utilized when the window image havingthe most favorable score/metric was captured.

The illumination selection circuitry 908 may also be configured to causethe photo sensor array 904 to capture 1508 a subsequent image using theselected set of illumination characteristics. The subsequent image maybe captured using a global shutter or a rolling shutter mode ofoperation. As indicated above, the test image(s) may include only aportion of a barcode. However, the subsequent image may include anentire barcode.

FIG. 16 illustrates another example of a method 1600 that may beperformed by the illumination selection circuitry 908 in accordance withthe present disclosure. The illumination selection circuitry 908 may beconfigured to cause the photo sensor array 904 to capture 1602 a singletest image 1210 of at least a portion of a barcode using a rollingshutter mode of operation. Windowing may be utilized, so that the testimage 1210 may be smaller than a full photo sensor array image.

The circuitry 908 may be configured to cycle 1604 through a plurality ofsets of illumination characteristics while the test image 1210 is beingcaptured, so that each set of illumination characteristics is utilizedfor a distinct time period while the single test image 1210 is beingcaptured and is not otherwise utilized while the single test image 1210is being captured. Consequently, the test image 1210 may include aplurality of window images 1212 a-b, where each window image 1212corresponds to a distinct band within the test image 1210, and whereeach window image 1212 corresponds to a distinct one of the plurality ofsets of illumination characteristics.

For example, during exposure of a first section 1214 a of the photosensor array 904, a first set of illumination characteristics (e.g.,direct, high intensity illumination) may be utilized. The window image1212 a may correspond to this first set of illumination characteristics.During exposure of a second section 1214 b of the photo sensor array904, a second set of illumination characteristics (e.g., angled, lowintensity, diffuse illumination) may be utilized. The window image 1212b may correspond to this second set of illumination characteristics.

Alternatively, during exposure of the first section 1214 a of the photosensor array 904, both the bright field illumination system 906 a andthe dark field illumination system 906 b may be activated, with thebright field illumination system 906 a powered at 60% and the dark fieldillumination system 906 b powered at 40%. During exposure of the secondsection 1214 b of the photo sensor array 904, both the bright fieldillumination system 906 a and the dark field illumination system 906 bmay be activated, with the bright field illumination system 906 apowered at 40% and the dark field illumination system 906 b powered at60%.

The circuitry 908 may also be configured to determine 1606 a selectedset of illumination characteristics. The selected set of illuminationcharacteristics may be the set of illumination characteristics thatyielded a window image 1212 having highest quality among the pluralityof window images 1212 a-b. The circuitry 908 may also be configured tocause the photo sensor array 904 to capture 1608 a subsequent imageusing the selected set of illumination characteristics.

FIG. 17 illustrates another example of a method 1700 that may beperformed by the illumination selection circuitry 908 in accordance withthe present disclosure. The circuitry 908 may be configured to cause thephoto sensor array 904 to capture 1702 a plurality of test images 1410a-b of at least a portion of a barcode. The plurality of test images1410 a-b may be captured using a rolling shutter mode of operation orusing a global shutter mode of operation. The plurality of test imagesmay correspond to different sections of the photo sensor array 904 (asshown in FIG. 14A), or to the same section of the photo sensor array 904(as shown in FIG. 14B).

The circuitry 908 may be configured to cycle 1704 through a plurality ofsets of illumination characteristics while the plurality of test images1410 a-b are being captured, so that each set of illuminationcharacteristics is used as the sole source of illumination for at leastone test image 1410. Each test image 1410 may therefore be considered tobe a window image 1412 corresponding to a particular set of illuminationcharacteristics. In other words, the plurality of test images 1410 a-bmay include a plurality of window images 1412 a-b, where each windowimage 1412 may correspond to a different one of the plurality of testimages 1410 a-b, and where each window image 1412 may correspond to adifferent one of the plurality of sets of illumination characteristics.

The circuitry 908 may also be configured to determine 1706 a selectedset of illumination characteristics. The selected set of illuminationcharacteristics may be the set of illumination characteristics thatyielded a window image having highest quality among the plurality ofwindow images. The circuitry 908 may also be configured to cause thephoto sensor array 904 to capture 1708 a subsequent image using theselected set of illumination characteristics.

FIG. 18 illustrates various components that may be utilized in a barcodereader 1802. Any of the barcode readers 100, 700, 800, 902 describedpreviously may include some or all of the components of the barcodereader 1802.

The barcode reader 1802 includes a processor 1804. The processor 1804may be a general purpose single- or multi-chip microprocessor (e.g., anARM), a special purpose microprocessor (e.g., a digital signal processor(DSP)), a microcontroller, a programmable gate array, etc. The processor1804 may be referred to as a central processing unit (CPU). Althoughjust a single processor 1804 is shown in the barcode reader 1802 of FIG.18, in an alternative configuration, a combination of processors (e.g.,an ARM and DSP) could be used.

The barcode reader 1802 also includes memory 1806 in electroniccommunication with the processor 1804. That is, the processor 1804 canread information from and/or write information to the memory 1806. Thememory 1806 may be any electronic component capable of storingelectronic information. The memory 1806 may be random access memory(RAM), read-only memory (ROM), magnetic disk storage media, opticalstorage media, flash memory devices in RAM, on-board memory includedwith the processor 1804, programmable read-only memory (PROM), erasableprogrammable read-only memory (EPROM), electrically erasable PROM(EEPROM), registers, and so forth, including combinations thereof.

Data and instructions may be stored in the memory 1806. The instructionsmay include one or more programs, routines, sub-routines, functions,procedures, etc. The instructions may include a single computer-readablestatement or many computer-readable statements. The instructions may beexecutable by the processor 1804 to implement one or more of themethods, operations, functions and/or procedures described above.Executing the instructions may involve the use of the data that isstored in the memory 1806.

The barcode reader 1802 may include several components that maycollectively be referred to as a camera 1808. Illumination components1810 within the camera 1808 may be activated so as to illuminate atarget area. The illumination components 1810 may be configured toprovide illumination having different illumination characteristics(e.g., by changing the intensity, wavelength, angle, and/or diffusioncharacteristics of the illumination), as described previously. Theillumination components 1810 may be included in a plurality of differentillumination systems having different illumination characteristics(e.g., a bright field illumination system, a diffuse bright fieldillumination system, and a dark field illumination system).Alternatively, the illumination components 1810 may be included within asingle illumination system that is configured to provide illuminationhaving different illumination characteristics. The illuminationcomponents 1810 may include light-emitting diodes (LEDs) and appropriatecontrol circuitry. One or more lenses 1812 within the camera 1808 mayfocus light reflected from item(s) within the target area (e.g., abarcode) onto a photo sensor array 1814. The photo sensor array 1814 maybe a solid-state photo-detecting device containing a relatively largenumber of light-sensitive pixels that are arranged in horizontal rowsand vertical columns. Read-out circuitry 1816 may electronically readthe pixels within the photo sensor array 1814 in order to obtain adigital image.

The barcode reader 1802 may include one or more user controls 1818 thatmay be used to provide user input. Examples of different kinds of usercontrols 1818 include one or more buttons, a touchscreen, a keyboard(actual and/or virtual), a microphone, a trackball, a lightpen, etc.

The barcode reader 1802 may include a display 1820. The display 1820 mayutilize any suitable image projection technology, such as a liquidcrystal display (LCD), light-emitting diode (LED), gas plasma,electroluminescence, etc. The display 1820 may be a touchscreen. Adisplay controller may also be provided, for converting data stored inthe memory 1806 into text, graphics, and/or moving images (asappropriate) shown on the display 1820.

The barcode reader 1802 may include one or more communication interfacesfor communicating with other electronic devices. For example, thebarcode reader 1802 may include a wireless modem 1822 that allows thebarcode reader 1802 to be connected to a wireless network.Alternatively, or in addition, the barcode reader 1802 may include awired communication interface 1824 (e.g., a USB interface).

As used herein, the term “determining” encompasses a wide variety ofactions and, therefore, “determining” can include calculating,computing, processing, deriving, investigating, looking up (e.g.,looking up in a table, a database or another data structure),ascertaining and the like. Also, “determining” can include receiving(e.g., receiving information), accessing (e.g., accessing data in amemory) and the like. Also, “determining” can include resolving,selecting, choosing, establishing and the like.

As used herein, the phrase “based on” does not mean “based only on,”unless expressly specified otherwise. In other words, the phrase “basedon” describes both “based only on” and “based at least on.”

One or more of the features, functions, procedures, operations,components, elements, structures, etc., described in connection with anyone of the configurations described herein may be combined with one ormore of the functions, procedures, operations, components, elements,structures, etc., described in connection with any of the otherconfigurations described herein, where compatible.

The steps and/or actions of the methods described herein may beinterchanged with one another without departing from the scope of theclaims. In other words, unless a specific order of steps or actions isrequired for proper operation of the method that is being described, theorder and/or use of specific steps and/or actions may be modifiedwithout departing from the scope of the claims.

The claims are not limited to the specific implementations describedabove. Various modifications, changes and variations may be made in thearrangement, operation and details of the implementations describedherein without departing from the scope of the claims.

What is claimed is:
 1. A barcode reader, comprising: a housing; a cameralocated within the housing configured to capture an image of a barcodewithin a field of view of the camera, the field of view being directedalong an optical axis; and an illumination system configured toilluminate the barcode while the camera captures the image of thebarcode, the illumination system comprising: at least one light source;and an optical substrate, not within the field of view of the camera,having front and back major surfaces arranged generally perpendicular tothe optical axis, and between which light introduced from the at leastone light source is transferred by total internal reflection primarilyin a direction transverse to the optical axis, wherein the opticalsubstrate comprises one or more extraction features configured toextract light from the optical substrate and into the field of view. 2.The barcode reader of claim 1, wherein the at least one light sourceintroduces light into an edge of the optical substrate between the frontand back major surfaces.
 3. The barcode reader of claim 1, wherein theat least one light source introduces light into the optical substratethrough the back major surface.
 4. The barcode reader of claim 1,wherein the optical substrate includes at least one aperture positionedaround the field of view of the camera.
 5. The barcode reader of claim4, wherein the optical substrate comprises an outer edge and an inneredge and the at least one light source introduces light into the outeredge of the optical substrate and the inner edge defines the aperture.6. The barcode reader of claim 5, wherein the optical substratecomprises an outer edge comprising a chamfered surface configured toreflect light onto a path relatively perpendicular to the optical axis.7. The barcode reader of claim 4, wherein the at least one light sourceintroduces light into an edge of the optical substrate between the frontand back major surfaces.
 8. The barcode reader of claim 4, wherein theat least one light source introduces light into the optical substratethrough the back major surface.
 9. The barcode reader of claim 4,wherein the optical substrate includes a reflective backing adjacent theback major surface.
 10. The barcode reader of claim 9, wherein thereflective backing is attached to the back major surface.
 11. Thebarcode reader of claim 4, wherein a shape of at least one of the frontmajor surface and the back major surface is at least one of concave,convex, and parabolic.
 12. The barcode reader of claim 11, wherein theshape of at least one of the front major surface and the back majorsurface is not symmetrical about a plane perpendicular to the opticalaxis.
 13. The barcode reader of claim 4, wherein the one or moreextraction features comprise variation of the surface topography of theback major surface.
 14. The barcode reader of claim 13, wherein thevariation of surface topography of the back major surface comprisesconvex and concave indentations and protrusions of the back majorsurface.
 15. The barcode reader of claim 4, wherein the illuminationsystem additionally comprises at least one secondary light source,wherein the light from the at least one secondary light source isemitted by the illumination system at an angle less than 45° from aplane perpendicular to the optical axis.
 16. The barcode reader of claim1, wherein the optical substrate includes a reflective backing adjacentthe back major surface.
 17. The barcode reader of claim 16, wherein thereflective backing is attached to the back major surface.
 18. Thebarcode reader of claim 1, wherein the illumination system additionallycomprises at least one secondary light source, wherein the light fromthe at least one secondary light source is emitted by the illuminationsystem at an angle less than 45° from a plane perpendicular to theoptical axis.
 19. The barcode reader of claim 1, wherein a shape of atleast one of the front major surface and the back major surface is atleast one of concave, convex, and parabolic.
 20. The barcode reader ofclaim 19, wherein the shape of at least one of the front major surfaceand the back major surface is not symmetrical about a planeperpendicular to the optical axis.
 21. The barcode reader of claim 1,wherein the one or more extraction features are within the opticalsubstrate.
 22. The barcode reader of claim 21, wherein the one or moreextraction features within the optical substrate is a variation in anindex of refraction of the optical substrate.
 23. The barcode reader ofclaim 22, wherein the variation in the index of refraction comprises atleast one of one or more particles within the optical substrate, and aplanar surface within the optical substrate.
 24. The barcode reader ofclaim 22, wherein the one or more extraction features are distributednon-uniformly throughout the optical substrate.
 25. The barcode readerof claim 24, wherein the one or more extraction features are distributedthroughout the optical substrate such that light is uniformly emittedfrom the front major surface of the optical substrate.
 26. The barcodereader of claim 24, wherein the one or more extraction features aredistributed throughout the optical substrate such that light isnon-uniformly emitted from the front major surface of the opticalsubstrate in a desired intensity pattern.
 27. The barcode reader ofclaim 21, wherein the at least one light source introduces light into anedge of the optical substrate between the front and back major surfaces.28. The barcode reader of claim 21, wherein the at least one lightsource introduces light into the optical substrate through the backmajor surface.
 29. The barcode reader of claim 21, wherein a shape of atleast one of the front major surface and the back major surface is atleast one of concave, convex, and parabolic.
 30. The barcode reader ofclaim 29, wherein the shape of at least one of the front major surfaceand the back major surface is not symmetrical about a planeperpendicular to the optical axis.
 31. The barcode reader of claim 1,wherein the one or more extraction features comprise variation of thesurface topography of the back major surface.
 32. The barcode reader ofclaim 31, wherein the variation of surface topography of the back majorsurface comprises convex and concave indentations and protrusions of theback major surface.